While wave-front conjugation systems employing photorefractive nonlinear devices can be operated in the laboratory, vibration encountered in real world environments washes out the holograms in the photorefractive devices because the response time of these devices is too slow.
It would be highly desirable to develop optical wave-front conjugation systems having high operating speeds and efficiencies at low optical power levels.
Recently there has been increased interest in the use of resonant atomic systems for performing optical wave-front conjugation. See P. F. Lino et al., Appl. Phys. Lett. 32, 813 (1978). This is because resonant atomic systems are inherently fast. However, resonant systems tend to have lower efficiency and greater optical power requirements than photorefractive crystals such as BaTiO.sub.3.